In river planning, either based on a 100-year or a 200-year flood frequency, river flow is always a necessary basis for the planning. When it is desired to directly obtain an actually measured flow, a lead fish must be utilized to measure the water depth during typhoon and flood. The water depth is then used to calculate a cross section area (A), and a current meter is used to measure current velocity (V). Finally, the flow (Q) is obtained using the formula Q=A×V.
The currently available current meter for measuring water depth and current velocity has a lead fish added thereto, so as to utilize the gravity to achieve the purpose of measuring water depth and current velocity. However, during typhoon and flood, since both the water depth and current velocity are increased, a heavier lead fish must be used. The heavy lead fish and the drag of water currents together form an amazing force, which not only consumes the measurer's body energy and threatens the measurer's safety in working, but also has great influence on the accuracy of measuring.
As having been affected by climate change, Taiwan region now has more rapid short-term climate change and increased frequency of extreme climate. The number of annual rainfall days is reduced while the probability of torrential rain and extremely heavy rain is largely increased, resulting in increased occurrence frequency of middle to high water level and water flow. The weight of lead fish increases with the increased current velocity and water depth to such an extent that can not be handled simply by manual operation. Sometimes, even a hoist is needed to perform the measuring. Therefore, increased labor cost is required while the measuring efficiency is low.